rite Immutable Class (String and all wrapper classes are immutable) Overloading and Overriding concept in details. (Basically, they confuse here) Abstract class in details (like it has constructor or not, can we create an object of the abstract class or not, etc) object class methods in details (like why we have hashcode() in the object class, notify-wait thread example) Serialization (we serialize the class contains 2 data member and after that, we replace one data member and new data member and then deserialize, then what will happen?) how to integrate Shiro/spring security in your project. how to use one-to-one, one-to-many, many-to-one and many-to-many mapping in MyBatis/Hibernate primary key vs foreign key (foreign key contains null or not) About your previous company project and current company project.